(a) Field of the Invention
The invention relates to a universal testing device for determining certain material properties of a sample.
(b) Description of Prior Art
Material testing refers to the evaluation of mechanical properties of solid materials by simultaneously measuring material deformation (displacement) and stress (force). The technical area is mature and highly developed with respect to industrial sized objects with dimension of centimeters or larger. When specimen dimensions encroach upon millimeters instrumentation and methods are less well developed, due to precision and control difficulties. When materials are soft in addition to small, technical difficulties also arise in eliminating noise from force signals.
Material testing systems are often developed with precise goals in mind. Thus some systems provide mechanical configurations appropriate for adhesion and tack tests (U.S. Pat. No. 5,438,863) for extrusion of thermoplastics in rheological testing (U.S. Pat. No. 4,680,958) and others for hardness and bonding tests of pharmaceuticals (U.S. Pat. Nos. 4,780,465, and 5,140,861). Common technical hurdles in these specific applications are precise control of displacement and low noise acquisition of force and displacement. These problems are overcome to varying degrees but generally insufficiently so in modern instruments. Also in spite of the underlying commonality in all material testing which is control and acquisition of force and displacement, instruments are often conceived and designed for the application of a limited number of tests where, for example, only one type of displacement is applied to obtain a certain force response upon which a particular analysis yields one characteristic material parameter. The limited flexibility of such systems is evident since proper mechanical and electrical design combined with algorithmic computer control of tests can in principle provide a universal system capable of executing the full range of material tests on small samples, as has been achieved for industrial sized objects. For example common measures of adhesion, tack, hardness, strength, modulus, viscoelasticity, plasticity etc. can all be obtained by parametric control of a limited number of fundamental tests such as ramp, stress relaxation, dynamic sinusoidal and creep tests.
In the biomedical domain of material testing, a particular need for testing samples in aqueous solutions under controlled environments of atmospheric gas composition and humidity arises. In the absence of material testing needs, these environments are generally provided by cell or tissue culture incubators. In the past, the need to perform material tests under these controlled environments has been addressed by developing testing chambers specific to the material testing apparatus to provide environmental control, since the material testing device is usually much too large to be placed in an incubator.
It would thus be highly desirable to be provided with a material testing instrument that would allow testing of these small specimens and that could be designed so as to fit inside a standard tissue culture incubator, thus adding to the universality of the device by including biomedical applications in their most standard format.